My guess is you're being trained to ride hunters. A lot of the"flaws" I'm seeing are what a lot of hunter riders are taught to do.
My background was in eventing, so the position we're taught is all about effect and staying safe. We're taught a defensive position, so I'd want to see your leg at the girth, not behind. It's isn't about shoulder, hip, heel alignment so much as finding your proper balance so when you start doing the big fences and a horse pops his back you can stay with it. I almost visualize sitting up straight, out of the tack, quiet with the horse between my legs and jumping up in front of me, so I can follow them and be with them so when we land I can be organized and prepare for the next one or at least not get in the way. When you get so far ahead it's hard to prepare and organize. I would do a ton of little grids like 2ft cross rails to help you prepare. With a trainer I'd do a series of 2ft cross rails with a series of 5 bounces to help you find your balance and help you so you don't fall forward. The progress isn't in the height of the fence or how you look over the fence but how well you ride between them and how effective you are.
When I evented I did a lot of wall sits, squats, and planks to strengthen my core and legs. I also would go on the stairs with the balls of feet touching the stairs and go up and down to increase strength and try to train my body, so it was easier to transfer it to in the saddle. Core strength has a lot to do with balance and is your center of control, so it really helps over and between fences. Another good one is yoga ball balance. I used to sit on a yoga ball with my shins over the ball, ankles under my butt and practice posting and two point like that to help my balance. If I couldn't do it I'd grab a ledge to help but it got pretty easy with practice.
I also still ride "dressage" between fences, as in I ride the balance and position the horse's shoulders between my legs. Steering with my outside thigh and rein. I still pay attention to the rhythm and consistency. I don't ride them in a dressage frame but seeking the connection and through, so they can use themselves more effectively. It really helps for riding your lines and riding your turns and corners. It helps a lot when your horse has a half halt to ride your distances better.
It takes time to develop all this and you should be pleased with yourself and where you are. And it isn't really your leg that's the problem, it's your upper body. By throwing yourself so far forward, it sends your leg straight back. Really remind yourself to sit up and back (not literally) but tell yourself to sit back more than you think you should and find your balance there. Let the horse put you into the position, you don't need to put yourself into position. Grab mane if necessary to help you find that balance. You're doing well! Keep it up!